Pubic Symphysis and Pelvis Anatomy

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Questions and Answers

What type of joint is the symphysis pubis?

Fibrous joint

Cartilaginous joint (correct)

Synovial joint

Hyaline joint

What is the purpose of the ligaments associated with the symphysis pubis?

To allow for more movement

To increase stability (correct)

To separate the bones

To reduce motion

Which muscles reinforce the anterior portion of the symphysis pubis?

Transversus abdominis, rectus abdominis, internal obliquus abdominis, and adductor longus (correct)

Only adductor longus

Only rectus abdominis

Only transversus abdominis

What is the normal angle of the lumbosacral joint?

140° Signup and view all the answers

What is the average pelvic angle of inclination?

60° Signup and view all the answers

What is the effect of pelvic tilt on lumbar lordosis?

An average change of 20° Signup and view all the answers

What is the term for the position of the pelvis between the extremes of anterior and posterior tilt?

Neutral pelvis Signup and view all the answers

During which time does motion in the pubic symphysis increase dramatically?

During pregnancy, especially at the time of birth Signup and view all the answers

What is the angle between a line joining the ASIS and PSIS, and a horizontal line?

11°± 4° Signup and view all the answers

What is the ideal pelvic alignment?

When the ASIS is on the same vertical plane as the symphysis pubis Signup and view all the answers

What is the main function of the sacroiliac joint?

Stress relief, load transfer, mobility, and stability Signup and view all the answers

What happens to the sacroiliac joints when unloaded, such as when lying down?

They move into a less stable, or counternutated, position Signup and view all the answers

What is the primary stabilizing force at the sacroiliac joint?

Gravity, stretched ligaments, and muscle activation Signup and view all the answers

What is the result of increased tension in the ligaments of the sacroiliac joint?

Increased compression of the joint surfaces Signup and view all the answers

What is the pubic symphysis similar to in terms of function?

The sacroiliac joint Signup and view all the answers

What is the close-packed position of the sacroiliac joint?

Full nutation Signup and view all the answers

What happens to the long posterior sacroiliac ligament during nutation?

It is slackened Signup and view all the answers

How do muscles stabilize the SI joints?

By all of the above Signup and view all the answers

What happens to the articular surface of the sacrum during nutation?

It glides inferoposteriorly relative to the innominate bones Signup and view all the answers

What happens to the articular surface of the ilium during counternutation?

It glides anterosuperiorly relative to the sacrum Signup and view all the answers

What is the result of the active locking mechanism?

Increased stability of the SI joints Signup and view all the answers

What is the purpose of the thoracolumbar fascia?

To attach muscles that stabilize the SI joints Signup and view all the answers

What is the level of the posterior superior iliac spines used to demonstrate?

Hypomobility of the sacroiliac joints Signup and view all the answers

What is the movement of the sacrum during counternutation?

Posterior rotation Signup and view all the answers

What is the movement of the ilium during nutation?

Anterior rotation Signup and view all the answers

What is the purpose of the sacrospinous and sacrotuberous ligaments?

To reinforce the SI joints Signup and view all the answers

Study Notes

Pubic Symphysis and Joints

Symphysis pubis is a fibrocartilaginous joint, allowing for slight movement between the pubic bones.
Ligaments associated with the symphysis pubis provide stability and support, preventing excessive movement.
The anterior portion of the symphysis pubis is reinforced by the rectus abdominis and external oblique muscles.

Lumbosacral Joint and Pelvic Angles

Normal angle of the lumbosacral joint is approximately 30 degrees.
Average pelvic angle of inclination is around 50 degrees.
Pelvic tilt affects lumbar lordosis; an anterior tilt increases lordosis, while a posterior tilt decreases it.

Pelvic Positioning and Mobility

The position of the pelvis between extremes of anterior and posterior tilt is called neutral position.
Motion in the pubic symphysis dramatically increases during pregnancy and childbirth.

Anatomical Angles

The angle between a line joining the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS) and a horizontal line is typically about 8 to 10 degrees.
Ideal pelvic alignment is when the ASIS and pubic symphysis are in the same vertical plane.

Sacroiliac Joint Functionality

Main function of the sacroiliac joint includes transferring weight from the upper body to the lower limbs effectively.
When unloaded, such as while lying down, sacroiliac joints relax, losing tension and slightly moving apart.

Stabilization Mechanisms

The primary stabilizing force at the sacroiliac joint is provided by the surrounding ligaments and the pelvic floor muscles.
Increased tension in the sacroiliac joint ligaments enhances stability but can also lead to discomfort if overstressed.

Functional Similarities and Positions

The pubic symphysis functions similarly to a hinge joint, allowing modest movement.
The close-packed position of the sacroiliac joint occurs when it is in full extension and pelvic stabilization is maximized.

Movement Dynamics of Nutation and Counternutation

During nutation, the long posterior sacroiliac ligament becomes taut, stabilizing the joint.
In nutation, the sacrum tilts forward while the ilium moves backward, creating a kinematic relationship that locks the joint.
During counternutation, the sacrum tilts backward, causing the ilium to move forward (relative to the sacrum).

Thoracolumbar Fascia and Anatomical Markers

The thoracolumbar fascia serves as a critical structure for stabilizing the lumbar region and providing support to surrounding muscles.
The level of the posterior superior iliac spines is typically used as a landmark for evaluating pelvic alignment and asymmetries.

Ligamental Functions

Sacrospinous and sacrotuberous ligaments stabilize the sacrum by restricting its movement and absorbing forces transmitted through the pelvis.

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Description

Test your knowledge of the pubic symphysis, a cartilaginous joint that connects the two ends of the pubic bones in the pelvis. Learn about its structure, function, and changes during pregnancy. Assess your understanding of the anatomy of the pelvis and its joints.